COUPLED-CLUSTER APPROACH TO CORRELATION IN SMALL MOLECULES: ENERGY VERSUS AMPLITUDE CORRECTED METHODS

The coupled cluster method, which is based on the exponential Ansatz for the wave operator, found a particularly fertile ground in quantum chemical investigations of the molecular electronic structure, where the many-electron correlation effects play a crucial role and where this approach became the method of choice, particularly when handling nondegenerate ground states. The objective of this contribution is to provide a brief historical perspective on some current challenges of the coupled cluster methodology and to outline some most recent attempts at their solution.